Crops such as melons and many weed species can harbor web-spinning spider mites and may become a source of infestation for an alfalfa seed crop. Also, spider mites may be harbored on the lower leaves of alfalfa plant throughout the year. Some insecticide applications, such as organophosphate or pyrethroids for lygus bug and stink bug control, can flare spider mite populations via destruction of predators or through hormoligosis (chemical stimulation of increased egg production). Many predators feed on spider mites including western flower thrips, minute pirate bugs, big eyed bugs and predaceous mites.

Abatement of sources of spider mites is important to reduce the potential for migration into the alfalfa seed field.

Abatement should include weed control and if possible removal or treatments of spider mites in surrounding crops such as melons.

Alfalfa seed production fields should be scouted twice weekly for spider mites beginning early season and continuing until the crop is prepared for harvest. Fields should also be monitored for spider mite predators and for other pests in the field. Proper scouting will lead to accurate assessments of spider mite pressure versus the predator population levels that may result in reduced use of chemicals through improved timing of applications. It may be practical to treat only portions of a field.

When web-spinning spider mites are present in an alfalfa field prior to seed production, a miticide spray may be needed to prevent damage leading to reduction of seed production. Stressing the alfalfa for water can stimulate bloom, but also favors the build-up of spider mites.

Historical knowledge of spider mite problems influences whether a grower controls spider mite populations immediately, or delays treatment for a while. Treat fields before populations reach damaging levels to maximize the efficacy of available chemicals. When possible, spot or strip treat localized spider mite infestations. Use ground application equipment when possible (prior to bee placement) to improve coverage. To prevent spider mite problems consider including a miticide with the first insecticide application for lygus bugs.

There is historical research trial evidence indicating that an application with a highly efficacious miticide early in the season with the first lygus bug treatment can prevent damaging population levels of spider mites for the remainder of the seed production season. Miticides registered for alfalfa seed production work best when used against low populations and none can resolve a significant spider mite problem.